31 Replies Latest reply: Mar 3, 2014 9:58 AM by Jared Conway

    Concrete nonlinear elastic

    Mousa D

      Hello,

       

      I have defined my own concrete material since surprisingly solidworks did not have concrete as a material. Then I have selected the linear elastic isotopic and defined my yield strength, young's modulus. After modelling my structure (Which is basically a simple two rectangles represtenting a flood wall. Base + wall ontop.)

       

      My first main problem was, after successfully getting a stress/displacements results, I have noticed that even If I increased the pressure by x10  I'd still get same displacement and stress, after setting it as true value. 

      Then again, going back to materials properties, when I change the yield strength from the previous 4.35N/mm2 I have set to 1N/mm2 .. still no changes at all.

       

      Would anyone please provide me with some explanation on what I am doing wrong, or why?

       

      Secondly, hopefully after I manage my first problem, I want to change my material properties into nonlinear elastic, which I have tried already with making my own stress/strain curve which looks similiar to the theortical concrete stress-strain curve. I noticed that after I try to run it, the material properties changes automatically back to linear elastic isotropic.

       

      Would highly appreciate any further help/suggestions and explantion on what I am doing wrong.

       

      Many thanks in advance

      Mousa.

        • Re: Concrete nonlinear elastic
          bill campbell

          Sounds strange. Here's a couple of things to try:

           

          1. In the cosmos (simulation) folder, RMB and click "Update All Components". This will for re-sync the cosmos and SW components. In the old days, we saved and re-opened the part to update components. May still have to do this.

           

          2. Make sure you make a copy of the material and paste it before changing any of the values. You can not change the library.

           

           

          Which Model Type are you using? non-linear elastic?

          • Re: Concrete nonlinear elastic
            Shaun Densberger

            "...have noticed that even If I increased the pressure by x10  I'd still get same displacement and stress..."

             

            Can you post an image of how your model is set up (geometry, boundary conditions, loads, etc.)

             

            "Then again, going back to materials properties, when I change the yield strength from the previous 4.35N/mm2 I have set to 1N/mm2 .. still no changes at all."

             

            Yield strength does not impact the numeric values for a linear elastic analysis. Yield strength is the point at which the material yields; the Young's Modulus defines the "stiffness" of the material. If you modify that value then you'll see different numeric values.

            • Re: Concrete nonlinear elastic
              Jared Conway

              1. only E is going to change the way the model behaves, and v in some cases. post some pictures of the displacements and stresses of both setups and also take a look at the reaction force on your restraint. since this sounds like a simple problem and user error to start, work on a simple block and post the model with both studies setup.

               

              2. what is the exact workflow that causes this problem? once you set a material, it will not change back to linear elastic. just make sure that you're using a nonlinear study.

              • Re: Concrete nonlinear elastic
                Mousa D

                Thank you, really appreciate the quick replies. My questions are as follows:

                • Using my first study, which is linear elastic isotropic for a concrete material that I have defined. (Included a screen shot below) As I am interested in the Y-axis Stresses, the results I have obtained seemed fairly reasonable. Yet, how can I be given results and different values for the Von Mises, even though it is set as linear elastic, surely there will not be plastic (Von mises) in my case? As a Von mises, I get yield strength as 4.3MPa, would that be my yield strength in the Y-axis stresses as well?

                 

                 

                 

                • In my second study, I have changed the simulation into nonlinear, and then went to the concrete material properties and changed it into nonlinear elastic, and created stress-strain that is fairly close enough to a concrete stress-strain curve. Only the compression part, or would I be able to draw the stress-strain for the tension part as well?
                • What is the difference between editting my material property to nonlinear elastic, and running my study as nonlinear elastic. As when I press apply material, it shows as nonlinear elastic, yet when I right click on edit material on the left column of the simulation, it shows it as linear elastic still. I have defined my stress strain curve as following, roughly estimated it, if there is a file or values that is more accurate to put in, please let me know.
                • I have not ran the nonlinear simulation yet as it apparently would take more than 5 hours, as I have tried it and it took about 30 minutes to reach 6%, so I cancelled it and wanted to be sure of all properties and such before running my simulation.

                 

                (My yield strength/tensile strength is 4.35N/mm2)

                  • Re: Concrete nonlinear elastic
                    Mousa D

                    I have copy/pasted 4 picture in my above post, I am not sure if it is visible to you or not.

                    • Re: Concrete nonlinear elastic
                      Jared Conway

                      Using my first study, which is linear elastic isotropic for a concrete material that I have defined. (Included a screen shot below) As I am interested in the Y-axis Stresses, the results I have obtained seemed fairly reasonable. Yet, how can I be given results and different values for the Von Mises, even though it is set as linear elastic, surely there will not be plastic (Von mises) in my case? As a Von mises, I get yield strength as 4.3MPa, would that be my yield strength in the Y-axis stresses as well? 

                       

                      >> you're expecting y stress to be the same as von mises?

                       

                      • In my second study, I have changed the simulation into nonlinear, and then went to the concrete material properties and changed it into nonlinear elastic, and created stress-strain that is fairly close enough to a concrete stress-strain curve. Only the compression part, or would I be able to draw the stress-strain for the tension part as well?

                       

                       

                      >> have you checked the documentation and the solidworks KB? i believe this is possible but it would be covered in these locations.

                       

                      • What is the difference between editting my material property to nonlinear elastic, and running my study as nonlinear elastic. As when I press apply material, it shows as nonlinear elastic, yet when I right click on edit material on the left column of the simulation, it shows it as linear elastic still. I have defined my stress strain curve as following, roughly estimated it, if there is a file or values that is more accurate to put in, please let me know.

                       

                       

                      >>what left column?

                       

                      >>file or values that are more accurate? this would come from your knowledge of the application. only you can answer this question.

                       

                      • I have not ran the nonlinear simulation yet as it apparently would take more than 5 hours, as I have tried it and it took about 30 minutes to reach 6%, so I cancelled it and wanted to be sure of all properties and such before running my simulation.

                       

                      >>this sounds like a good idea. my recommendation would be to start with just a block and get a hang of how solidworks simulation works first. go through the tutorials, go through the help and thne if you can, take your reseller's training to get a good introduction to the interface. and if they have it, go through some one-on-one training. here at hawk ridge systems we offer both to our customers to give them the best chance of quick success with solidworks simulation.

                      • Re: Concrete nonlinear elastic
                        Shaun Densberger

                        "As I am interested in the Y-axis Stresses, the results I have obtained seemed fairly reasonable. Yet, how can I be given results and different values for the Von Mises, even though it is set as linear elastic, surely there will not be plastic (Von mises) in my case? As a Von mises, I get yield strength as 4.3MPa, would that be my yield strength in the Y-axis stresses as well?"

                         

                        There's many different failure theories used in solid mechanics, but the two most common used in general FEA are:

                         

                        1. Von-Mises Yield Criteria
                        2. Mohr–Coulomb Theory

                         

                        One key difference between the two is that von-Mises is good for ductile materials (steel, aluminum, etc.), while Mohr-Coulomb is good for brittle materials (cast iron, concrete, etc). Another important note is that von-Mises is a scalar quantity, meaning that it doesn't have a direction associated with it (hence a negative von-Mises stress being meaning).

                         

                        "In my second study, I have changed the simulation into nonlinear, and then went to the concrete material properties and changed it into nonlinear elastic, and created stress-strain that is fairly close enough to a concrete stress-strain curve. Only the compression part, or would I be able to draw the stress-strain for the tension part as well?"

                         

                        I've never really worked with brittle materials before, but I know that for ductile materials (like steel), the strain-strain curve is the same for tension or compression within the elastic region, but different in the plastic region. This link is worth reading. http://www2.ce.metu.edu.tr/~ce581/docs/Lecture%20Notes/Chapter%201/1_1_MATERIAL_BEHAVIOR.pdf

                         

                        "What is the difference between editting my material property to nonlinear elastic, and running my study as nonlinear elastic. As when I press apply material, it shows as nonlinear elastic, yet when I right click on edit material on the left column of the simulation, it shows it as linear elastic still. I have defined my stress strain curve as following, roughly estimated it, if there is a file or values that is more accurate to put in, please let me know."

                         

                        I don't use SW simulation that much, but I'm almost positive that if you want to run a non-linear material model, you need to run a non-linear analysis, which mean creating a new analysis and selecting non-linear static. Others can correctly me if I'm wrong.

                         

                        Non-Linear Static.PNG

                         

                        "I have not ran the nonlinear simulation yet as it apparently would take more than 5 hours, as I have tried it and it took about 30 minutes to reach 6%, so I cancelled it and wanted to be sure of all properties and such before running my simulation."

                         

                        Just be warned that non-linear can be rather difficult and somewhat trial and error based when you're starting out with it.

                      • Re: Concrete nonlinear elastic
                        Mousa D

                        Here is a file that contains all pictures taken, Linear, nonlinear, and the error I get when I run nonlinear. (As a PDF)

                          • Re: Concrete nonlinear elastic
                            Martijn Loonen

                            See images on how to add files. Go to the advanced editor, below click add files.

                            Maybe save the word file as pdf, since not everybody has the same Word versionNaamloos.png

                            • Re: Concrete nonlinear elastic
                              Shaun Densberger

                              I looks like you've defined a non-linear dynamic analysis. While you could solve this type of problem with non-linear dynamics, I would recommend that you stick with non-linear static. Try you're model again was a non-linear static analysi. If the analysis fails, try cutting your load (try 1% of your current load) and see if it'll solve. If it doesn't, then try replacing your pressure load with an enforced displacement and re-running the analysis. Let us know the results of all of this.

                                • Re: Concrete nonlinear elastic
                                  Jared Conway

                                  I mousa, i'd concentrate on starting simple.

                                   

                                  get the hang of a linear static, understand what it means and the assumptions that go along with it.

                                   

                                  create posts for each issue you run into and try attacking them one at a time (many to one vs one to many is a lot easiest to approach)

                                   

                                  then build up as your knowledge increases

                                   

                                  also if you can, i'd highly recommend involving your reseller who can provide training in the basics of simulation and then technical support in a quicker fashion than through the forum

                                  • Re: Concrete nonlinear elastic
                                    Mousa D

                                    Hello Jared, thank you for your reply.  I have defined a non-linear static analysis, and then ticked the 2D simplification but did not understand what values I should put in, so unticked it and continued.  As you have mentioned it failed when I've put my pressure as 2.7N/mm2 from the first iteration saying "PCGLSS0139:Matrix is Singular or Indefinite*****************" , then changed my pressure into 2.7N/m2 and it solved really quick. (Even though the stresses in Y-axis that I am interested in were all zeros.) What would be my problem and how can I fix it please?

                                     

                                    Many thanks in advance.

                                      • Re: Concrete nonlinear elastic
                                        Jared Conway

                                        matrix is singular = not enough restraints in your problem or your load is too high potentially

                                         

                                        going to nonlinear and 2d without having the fundamentals of static is probably relatively challenging. i'd recommend starting with a block in a static analysis. get that to work. then you can move from the block to your model with a fixed restraint. then your loading. then nonlinear. if you want to throw 2d in the mix. go from block to 2d and then your geometry..etc.

                                    • Re: Concrete nonlinear elastic
                                      Jared Conway

                                      what are you trying to show in this doc?

                                    • Re: Concrete nonlinear elastic
                                      Mousa D

                                      Hello, I managed to over come few of the problems I had earlier.  Defining my own material (Concrete) with reference to steel, I was interested in the tension curve, knowing that for steel the tension and compression stress-strain curves are equal, I defined compression stress-strain curve as the tension one. Just for reference, does the software enable you to make both the stress-strain curve for tension and compression, or is it just compression?